1. Field of the Invention
The present invention relates to a liquid container, a liquid supplying apparatus, and a recording apparatus for supplying a liquid such as ink to a pen or recording head as a recording section, for example, in an efficient and stable manner, and to an ink jet cartridge.
2. Description of the Related Art
Ink jet recording apparatuses that form an image on a recording medium by applying ink that is a liquid to the recording medium using a liquid consuming or using apparatus such as an ink jet recording head include apparatus that form an image by ejecting ink while moving a recording head relative to a recording medium and apparatus that form an image by ejecting ink while moving a recording medium relative to a fixed recording head conversely.
Methods of supplying ink to a recording head used in such an ink jet recording apparatus include a method referred to as on-carriage method in which an ink tank is integrally or separably mounted to a recording head that is carried by a carriage to be moved back and forth (main scanning) and in which ink is directly supplied from the ink tank to the recording head. There is another method referred to as tube supply method in which an ink tank is fixed in a region of a recording apparatus other than a carriage as a body separate from a recording head carried by the carriage and in which ink is supplied by coupling the ink tank and the recording head through a flexible tube. The method includes a configuration in which a second ink tank to serve as an intermediate tank (sub-tank) between an ink tank (main tank) and a recording head is mounted on the recording head or a carriage and in which ink is directly supplied from the second ink tank to the recording head.
According to those methods, an ink tank to supply ink to a recording head directly is provided with a mechanism for generating an adequate negative pressure in a range in which the negative pressure is in equilibrium with a pressure in the recording head to hold meniscuses formed at an ink ejecting section thereof to prevent the ink from leaking from the ink ejecting section satisfactorily and in which an ink ejecting operation of the recording head can be performed.
In a negative pressure generating mechanism of this type, a porous member such as a sponge that is impregnated with ink to be held thereby is contained in an ink tank, and an adequate negative pressure is generated by an ink holding capacity of the same.
In another mechanism, a bag-shaped member formed from a material such as rubber having an elastic force and generating a tension in the direction of increasing the volume thereof is charged with ink as it is, and the tension generated by the bag-shaped member exerts a negative pressure to the in therein.
In still another mechanism, a bag-shaped member is formed using a flexible film, and a spring for urging the film in the direction of increasing the volume of the bag-shaped member is bonded to the interior or exterior of the same to generate a negative pressure.
In any of the above mechanisms, however, the negative pressure tends to increase as the amount of ink in the ink tank decreases, and it becomes impossible to supply ink to a recording head stably when the level of the negative pressure exceeds a predetermined value. This results in a problem in that the ink tank becomes unusable before the ink is completely used up.
For example, there is Japanese Patent Application Publication No. 3-024900 (1991) which discloses a structure of an ink tank of a type which is constituted by a flexible enclosed bag-shaped member that directly contains ink therein and that can be deformed according to the amount of contained ink and in which a spring member is provided in the bag-shaped member. Since the negative pressure is basically determined such that the spring force and a force resulting from the negative pressure (or a difference between the atmospheric pressure and the negative pressure) are balanced with each other, the negative pressure in the bag-shaped member increases as the deformation of the spring proceeds with the deformation of the bag-shaped member as a result of ink consumption. This may result in a problem in that the negative pressure increases beyond a proper range in which an ink ejecting operation of the recording head can be performed to prevent the formation adequate meniscuses at the ink ejecting section of the recording head or in that the ink can not be satisfactorily supplied to the recording head. This also disallows the ink to be used completely.
Some ink tanks have a configuration in which ink is contained in a bag-shaped member, and the material and shape of which are appropriately selected to generate a negative pressure by the bag-shaped member itself and which becomes flat with no space left therein when the ink is completely used up, but there are limitations on the shape of such a bag-shaped member. Therefore, when such an ink tank is configured to be contained in a box-like housing, the configuration of the bag-shaped member does not fit the interior of the housing completely even when it is charged with ink, and the volumetric efficiency of the ink tank is low with respect to the entire space available therein. Such a bag-shaped member also has a problem in that its performance of supplying ink to a recording head can be reduced and in that it can make an ink ejecting operation of a recording head unstable when ink is nearly used up because of a high negative pressure.
Several mechanisms have been proposed as follows to prevent magnitude of a negative pressure being too much greater than the predetermined level.
For example, Japanese Patent Application Laid-open No. 7-125240 (1995) and Japanese Patent Application Laid-open No. 7-125241 (1995) have disclosed mechanisms in which a hydrophobic film and a tubular vent port are provided in a tank, and a spherical body is disposed in the tube to introduce air into the tank when a negative pressure therein increases. That is, those publications have disclosed mechanisms which have a tubular vent port (boss) that establishes communication between the outside and inside of a container and in which spherical body having an outer diameter smaller than an inner diameter of the boss is attached to a plurality of projecting ribs provided on an inner wall of the boss to form a substantially annular orifice with the spherical body and the boss. The size of such an orifice is chosen such that a small amount of ink is kept in the orifice as a liquid seal because of the capillarity of ink. The orifice is configured such that a negative pressure in the container overcomes the capillarity of ink to disable the liquid seal when it nearly reaches the limit of an operating range of the recording head.
Japanese Patent Application Laid-open No. 6-183023 (1994) has disclosed a mechanism in which a plate-like member having a hole and a plate having a protrusion are provided in a face-to-face relationship in an ink bag constituted by a flexible sheet with a spring member disposed between the plates and in which the protrusion enters the hole when an internal negative pressure exceeds a predetermined value to separate the plate having the hole and the flexible sheet from each other, thereby introducing air in the tank. In this mechanism, the plate having the hole and the flexible sheet come into tight contact with each other after air is introduced, and leakage of ink is prevented by an ability for holding ink meniscuses or a liquid seal formed between those elements.
However, those methods require a plurality of parts in a region where air is introduced, and the structure of such a region has therefore become complicated.
When a pressure in a container T having a certain amount of air introduced therein becomes extremely high as a result of an ambient change (a reduction of the atmospheric pressure or a temperature rise) as shown in FIG. 1A, ink is pushed out from the container as shown in FIG. 1B, which can result in leakage of ink through an ink ejection port N or a vent hole A when the container is used in an ink jet recording head. When a liquid is contained in a bag-shaped member constituted by a flexible sheet, although expected is a certain degree of buffering effect that moderates an increase of a pressure therein by accommodating expansion of air which results in a pressure reduction, such an effect is limited.
In the configuration disclosed in Japanese Patent Application Laid-open No. 7-125240 (1995) or Japanese Patent Application Laid-open No. 7-125241 (1995), an enclosed system is established by balancing a force originating from ink meniscus formed in the region of the annular orifice and a negative pressure provided by the spring. Although the mechanical configuration is relatively simple, it is insufficient in stability in maintaining the enclosed system. Specifically, a problem arises in that contained ink can leak out because of breakage of a liquid seal that is attributable to various conditions such as a difference between air pressures inside and outside the container, a reduction of the viscosity of ink resulting from an increase in the temperature of ink, a shock or drop that occurs when the ink tank is handled alone, and acceleration that occurs during main scanning according to the serial recording method, in particular. Further, a liquid seal is vulnerable to humidity changes such as drying, which causes variations in the operation of introducing air bubbles and consequently reduces the capability of supplying ink to a recording head and hence the quality of recording.
It is assumed that the above publications have disclosed configurations in which an entrance maze serving as an overflow container and ensuring a humidity gradient is provided contiguously with a boss in order to prevent such problems, but the configurations become complicated accordingly. Further, since the other end of the channel in the form of a maze is always in communication with the atmosphere, a certain degree of ink evaporation is unavoidable.
When ink in the container is used up, outside air is abruptly introduced to eliminate the negative pressure in the container. This can cause ink remaining in the region of the recording head to leak out through the ejection port, and the residual ink can leak out through the annular orifice that no longer forms meniscus.
Further, in those examples of the related art, there is provided an opening section for directly introducing the atmosphere into an ink tank. As a result, the quantity of gases in the ink tank becomes relatively great in a region in the ink tank where ink is nearly used up depending on the size and position of the opening section, which can result in incomplete holding of meniscuses at the ink ejection port or opening section when the negative pressure is eliminated as a result of introduction of the atmosphere and can therefore lead to leakage of ink or incomplete introduction of the atmosphere.
In addition, breakage of a liquid seal can occur because of various conditions such as a difference between air pressures inside and outside the container, a temperature rise of drop, a shock or drop that occurs when the ink tank is handled alone, and acceleration that occurs during main scanning according to the serial recording method, in particular. This results in a problem in that air can be introduced or ink can leak out conversely even when a pressure in the container has not reached a predetermined value. Further, such conditions can vary depending on the designs of the recording head and ink tank or physical properties of ink, and a problem arises also in that designing must be adequately carried out in accordance with the shape and dimensions of the opening section and the basic configuration of the negative pressure generating mechanism depending on each mode of use.
The above ink tank utilizing a liquid seal for introducing air creates problems such as a reduction of freedom in designing a recording apparatus in addition to problems inherent in it as described above.
Specifically, it is not easy to configure such a liquid seal section as an element separate from an ink tank by making it detachable from the ink tank, for example. In case that the liquid seal section is provided as a separate element, a complicated process or apparatus configuration will be required when attaching the element to an ink tank directly or connecting it to the ink tank indirectly through a tube in order to form preferable meniscus in an annular section as described above taking factors such as a difference between pressures inside and outside the ink tank into consideration.
When the liquid seal section is provided in a position apart from an ink tank with a tube interposed therebetween, the tube must be filled with ink to form meniscus at the liquid seal section. However, the ink in the tube will be returned to the ink tank when air is introduced through the liquid seal section, and a complicated process or configuration will be required to refill the tube with ink thereafter as described above.
The technique disclosed in the Japanese Patent Application Laid-open No. 6-183023 (1994) employs a structure in which air is introduced through a microscopic gap between a thin plate-like member and a flexible sheet. This has resulted in another problem in that a negative pressure becomes unstable when air is introduced because the force for causing separation as described is changed by a capillary force that is generated when a liquid enters the gap.
Further, in order to provide a sufficient buffering function, a member that has extremely low rigidity and that is easy to deform is used as the flexible member for moderating an internal pressure of a container by substantially increasing the volumetric capacity of the container through the deformation of the flexible member itself when the pressure of a gas (air) in the container increases as a result of a temperature rise.
However, since a material having low rigidity used as such a flexible member has a small thickness and exhibits high permeability against gases in general, it is likely to allow a gas to penetrate into a container because of an osmotic pressure of the gas. This has resulted in the possibility of insufficient performance of the buffering function when a liquid is kept in the container for a long time because a gas (air) can penetrate into the container in a quantity that cannot be handled by the buffering function for absorbing expansion of the gas in the container. Therefore, it has been necessary to use a quite expensive material having a metal deposited thereon as the material of the flexible member in order to achieve low rigidity and a reduction in gas permeability at the same time.